1. Field of the Invention
The present invention relates to a method for the realization of an implant prosthesis as well as to parts which are applied thereby.
These parts relate more especially to a ring combination which principally consists of a positioning ring for the correct positioning in relation to each other of the parts to be connected to each other, namely, on the one hand, the dental implant and, on the other hand, the bridge structure, and a correction ring which, after the bridge structure has been realized, allows possible inaccuracies between the dental implant and the realized dental bridge structure to be adjusted and to be corrected.
2. Discussion of the Related Art
It is known that in dental prosthetics methods exist for attaching a prosthesis to a toothless jaw in a permanent manner, whereby these new methods can offer a good alternative when conventional removable prostheses do not suffice functionally or psychologically.
These known methods for attaching a prosthesis to a toothless jaw, can among others consist of the implantation, after the opening of the mucosa or mucous membrane, of a screw shaped structure of a biocompatible metal, for example of titanium, in the bone of the jaw. The the screw shaped structure is completely embedded in the bone, after which the mucosa or mucous membrane is sutured and a waiting time of up to approximately 6 months is taken into account in order to allow the bone to coalesce and osseointegrate with the implanted screw shaped structure.
After this resting period the mucosa or mucous membrane is again opened. An elongation piece is screwed onto the implant, and the mucous membrane is sutured around this elongation piece.
Such an elongation piece is provided with an internal screw thread into which an actual prosthesis can be screwed.
The level of success of such osseointegration is very high and is scientifically and clinically accepted.
Depending upon the quality of the bone, several implants can be installed. A bridge structure, for example in the form of a tooth crown or a U-shaped bar structure, can be screwed to these implants.
The metal structure is made in a plaster model by a dental technician according to the lost wax method known in industry, whereby this plaster model must represent an accurate copy of the tissues and the implants of the patient.
With the intention of obtaining an accurate copy of this mouth layout, auxiliary molding parts are screwed into the respective implants. After this an elastic molding material, such as for example, silicone, is applied, so that a negative is obtained of the tissues and of the auxiliary molding parts.
The aforementioned auxiliary molding parts are thereafter screwed out and screwed together with a so-called analog or dummy.
The auxiliary molding part side is subsequently replaced in the mold into which hard plaster is cast so that a positive copy of the mouth layout is obtained.
The analogs or dummies then sit in the location of the implants.
In this manner the work model is obtained for the dental technician.
Three often utilized techniques exist for realizing a metal bridge structure.
A first method consists in screwing down a casting cylinder onto the analogs. After this, these cylinders, are surrounded by wax and connected to each other, in order, according to the lost wax method, to surround these cylinders with metal and to connect them to each other.
A second method consists in that use is made of a synthetic material replica of the cylinders which are connected together in order to form a homogeneous metal structure according to the lost wax method.
The third method finally consists in that metal connecting elements are soldered between the cylinders.
The aforementioned cylinders can realized in any material, but use will preferably be made of cylinders in gold or in synthetic material.
The great technical problem of inaccuracy arises with all these techniques. Indeed the permitted tolerances with a similar tooth crown on ground natural elements are far greater than with implants.
Namely, with implants, no periodontal ligament exists such as is the case with natural elements.
From this it follows that inaccuracies, even in the micron range, can lead to abnormal stress zones when these are not discovered and corrected by the dentist.
Such stress zones can manifest themselves in various forms, namely through bone resorption, through the failure of osseointegration, through the loosening or breaking of screws or through the breaking of prosthetic bridge structures.
These inaccuracies can be caused, either during the molding technique, for example by not screwing the analogs tight enough, or because of the intercondylar distance increase during the molding of the lower jaw with open mouth, or even through the change of shape of the molding material or of the hard plaster, which is described as an incorrect work model, etc.
As is known, the adjustment of a U-shaped bridge structure is particularly difficult with respect to several implants, thus, in practice, it is very often necessary to grind through the bridge structure and subsequently to reattach the parts by soldering, which has the great disadvantage that through the local heating of the metal bridge structure and/or the shrinkage in the solder connection, new inaccuracies appear.
In order to avoid these inaccuracies, in other words, in order to avoid soldering or integral casting, the use has already been suggested of composite materials, such as among others described in the European patent application no. 0.161.295 and in the German patent application no. 35 25 298.
With the same intention, it has already been suggested to connect the prosthetic parts to each other by gluing, such as for example described in:
Gerhard Geiger, "Geschiebe-Technik", Munich 1982, pgs 167 to 171; PA1 "Das Dental Labor", Heft 3/82, pgs. 301 to 302.
In the article "Direct assembly framework for osseointegrated implant prothesis" by Grady C. Sellers, D.D.S. from "The journal of prosthetic Dentistry", Dec. 1989, volume 62, number 6, pgs. 662-668, a method is further described whereby parts for an implant prosthesis are intraorally connected to each other by means of composite, to avoid stress through inaccuracies, on the one hand, and to avoid additional correction techniques, on the other hand.
With this known technique a metal support ring is installed on the implant, after which a metal structure is realized over these support rings.
The support rings and the metal structure are subsequently intraorally connected to each other by means of a composite glue.
This technique has among others a disadvantage that the metal structure, which is mounted to fit precisely around the support rings, must be ground on the inside when a distortion or inaccuracy occurs.
The size of this distortion or inaccuracy can only determined after the grinding.
When it is finally decided to grind through the bridge structure and to solder the parts to each other, the individual correct fit no longer exists.